Conventionally, there is disclosed a radar which receives a reflection signal of a transmission signal reflected on an object using one reception antenna and detects a distance up to the object and a relative velocity with respect to the object based on the transmission signal and the received reflection signal (for example, see Japanese Laid-open Patent Publication No. 2012-198070). In addition, there is disclosed a radar which receives the reflection signal from the object using a plurality of reception antennas and improves the detection accuracy of the object by detecting the object using the plurality of received reflection signals.
The radar having the plurality of reception antennas mixes the reflection signals received by the reception antennas and the transmission signal to generate a plurality of beat signals, performs a predetermined signal processing on each beat signal, and then converts the analog beat signal into a digital beat signal. Then, the radar performs the fast Fourier transform on the digital beat signal, and detects the distance up to the object and the relative velocity with respect to the object by analysis on the frequency of the converted signal.
The radar includes a plurality of signal processing units which perform a predetermined signal processing on the plurality of beat signals in parallel. Each signal processing unit is designed not to cause a variation in characteristics to the upmost, but the variation is caused in some cases. In such a case, the radar generates a relative phase error between the beat signals after the signal processing of each signal processing unit, and makes the detection accuracy of the object lowered.
As a method of suppressing the reduction of the detection accuracy as described above, for example, there is a method in which a test for detection of the object is performed on the object placed at a position away from the radar by a predetermined distance, and a relative phase error value is calculated from detection data and used as a correction value of the beat signal.
However, the distance to a detectable object is extended. Thus, it is difficult for recent radars to perform the test for the detection of the object at a maximum detectable position in a limited manufacturing space. Therefore, the detection accuracy of the object at a remote place may be reduced.